US3716801A - Amplifier with improved avc circuit - Google Patents

Amplifier with improved avc circuit Download PDF

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Publication number
US3716801A
US3716801A US00052814A US3716801DA US3716801A US 3716801 A US3716801 A US 3716801A US 00052814 A US00052814 A US 00052814A US 3716801D A US3716801D A US 3716801DA US 3716801 A US3716801 A US 3716801A
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United States
Prior art keywords
amplifier
avc
circuit
time constant
voltage
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Expired - Lifetime
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US00052814A
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English (en)
Inventor
W Minner
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Telefunken Electronic GmbH
Original Assignee
Licentia Patent Verwaltungs GmbH
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Assigned to TELEFUNKEN ELECTRONIC GMBH reassignment TELEFUNKEN ELECTRONIC GMBH ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: LICENTIA PATENT-VERWALTUNGS-GMBH, A GERMAN LIMITED LIABILITY COMPANY
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Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G3/00—Gain control in amplifiers or frequency changers
    • H03G3/20—Automatic control
    • H03G3/30—Automatic control in amplifiers having semiconductor devices
    • H03G3/3005—Automatic control in amplifiers having semiconductor devices in amplifiers suitable for low-frequencies, e.g. audio amplifiers

Definitions

  • No.: 52,814 An improved AVC circuit for an alternating voltage amplifier which prevents over-control, and thus temporary blocking of the amplifier circuit, upon the oc- [30] Foreign Applicauon Priority Data currence of a sudden large increase in the amplitude July 7, 1969 Germany ..P 19 34 306.7 of the input signal to the amplifier.
  • the control voltage generating arrangement of the AVC circuit is con- [52] U.S. Cl ..330/29, 330/141 structed so that the time constant of the control volt [51] Int. Cl.
  • the present invention relates to alternating voltage amplifiers provided with automatic volume control (AVC) circuits. More particularly, this invention relates to an alternating voltage amplifier having an improved automatic volume control circuit whereby temporary blocking of the amplifier due to overcontrol as a result of a sudden increase or jump in the alternating voltage input signal to the amplifier is avoided.
  • AVC automatic volume control
  • alternating voltage amplifiers with automatic volume or gain control it often occurs that due to a sudden jump or increase in the amplitude of the alternating voltage input signal to the amplifier, the amplifier is temporarily completely blocked, i.e., no output signal can be provided. This may occur, for example, when recording audio signals and particularly voice signals with tape recorders which are provided with an automatic gain control to prevent overloading of the tape.
  • AVC automatic volume or gain control
  • the cause for the temporary blockage of the amplifier is that the member of the amplifier which is controlled by the AVC voltage (i.e., the controlled amplifier stage) has a time constant t,, due to its capacitances and resistances, which is not negligibly small when compared with the time constant r, of the control voltage generator in the AVC circuit, so that the controlled member or stage of the amplifier can not follow the above-mentioned jump or increase in the input signal fast enough. This inability of the controlled member or stage of the amplifier to respondquickly enough results.
  • the amplifier With a sudden jump in the alternating input voltage signal the amplifier furnishes acorrespondingly high alternating output voltage signal, which output signal is fed to the control voltage generator of the AVC circuit which provides an AVC controlvoltage proportional to the amplifier output signal, and-with a time constant which is applied to the controlled member of the amplifier. Because of its time constant 1, the amplifier causes the amplitude of the alternating output voltage signal to follow the control voltage only after a delay, so that a control voltage is produced which is higher than that required to compensate for the instantaneous alternating input voltage signal. Due to the large amplitude of the control voltage, the amplification of the amplifier is correspondingly reduced so that the amplifier may become blocked. This blocking of the amplifier remains until the control voltage has returned to its nominal value. The time required for this process is determined by the discharge time constant of the capacitor in the AVC circuit which provides the control voltage.
  • control voltage generator utilized in the AVC circuit has a time constant which automatically increases with increasing alternating input voltage to such an extent that, independent of the value of the alternating input voltage, no over-control takes place and the above-mentioned blocking of the amplifier is thus avoided. In this way the generation of the control voltage information is slowed down until the AVC control circuit has been stabilized.
  • time constant 2 of the control voltage generator must automatically increase starting from a predetermined alternating amplifier output voltage in proportion with this alternating output voltage.
  • the control voltage generator of the AVC circuit comprises a transistor connected as a collector detector circuit with the above-mentioned charging capacitor connected in series with its emitter current path and an ohmic resistor connected in its collector current path to limit the charging current to the capacitor.
  • FIG. 1 is a block diagram illustrating a conventional amplifier with an AVC circuit.
  • FIG. 2 is a schematic diagram of a control voltage generator for the AVC circuit according to the preferred embodiment of the invention.
  • FIG. 1 there is shown an amplifier V with settable member or controllable stage S whose time constant t, is formed byinternal RC elements and/or by the coupling capacitor C and resistor R for the supply of the AVC control voltage.
  • the amplification of the amplifier is'a function of the control voltage V which is derived in the control voltage generator R having a time constant t from the alternating output voltage E, of the amplifier.
  • This alternating output voltage signal E is fed to the input of the AVC control voltage generator R via a capacitor C
  • the known amplifiers of this construction with auto matic volume control operate faultlessly only when the time constant t, of the amplifier is substantially less than the time constant of the AVC control voltage generating circuit R and thus may be considered negligible.
  • a sudden increase of the input voltage E, to twice its value will be compem sated in a time period T which depends only on the time constant t of the control voltage generator.
  • a sudden jump increase in the input voltage E, to times its value, however, is compensated in approximately one one-hundredth T since the voltage offered to the control voltage generator R is also increased 100 times, but the control voltage V required to change the amplification of the amplifier requires only a very siight adjustment with the large slope of the control curve.
  • the setting member or controlled stageS has a time constant I, which is not negligibly small when compared with the time constant t
  • the time constant of the control voltage generator is assumed to be so selected that with low input voltages E; an increase of E, to twice its value is compensated in the above-mentioned time T under consideration of the time constant t of the setting member S.
  • an increase in the input voltage E, and thus momentarily also in the output voltage E of the amplifier (assuming linear amplification) to 100 times its value also increases the time constant by 100 times so that the control of the sudden change in the input voltage E, again occurs in the time period T (not as previously in one one-hundredth T). Blocking of the amplifier is thus avoided since the effective time constant it, of the control voltage generator R is now substantially larger than the time constant t, of the setting member or controllable stage 8.
  • FIG. 2 shows an example for the circuitry for a control voltage generator R according to the present invention which differs by the provision of resistor R, in collector current path of the transistor 7 from the conventional design of a collector detector circuit.
  • the alternating voltage E is fed to the base of the transistor T via a capacitor C and a resistor R connected in series.
  • the charging current I flows from the source of operating voltage V via the collector-emitter circuit path of transistor T into the charging capacitor C connected to the emitter of the transistor T and there generates the control voltage V
  • the discharge resistor R for capacitor C is also shown.
  • This resistor R is generally of such a size that it need not be considered in determining the charging time constant of the capacitor ,C in the conventional design of a collector detector, (i.e., R is shortcircuited) the maximum charge current I is 1 maxl z-Eol a' (i) where B is the current amplification factor of the transistor T in common-emitter connection and the factor one-half considers that a charging current flows only during the positive half-cycle of E,,.
  • the charging time constant 1, of the control voltage generator R is t ⁇ L as long as the alternating voltage amplitude of the amplifier output signal is 0 VB a)/( 2) (5) if the amplitude exceeds this value, then according. to the invention 2 11.
  • E 2 the charging time constant
  • said AVC circuit comprises: a collector-detector circuit including a transistor which is arranged only in the AVC-voltage signal path but not in the forward signal transmission path of said amplifier,
  • said transistor having its base connected to the output of said amplifier and its emitter-collector circuit connected across a source of operating d.c. potential; a charging capacitor connected in the emitter circuit path of said transistor for furnishing the AVC circuit control voltage; and means for limiting the charging current to said capacitor comprising an ohmic resistor connected in the collector circuit path of said transistor, whereby the time constant of said AVC circuit is increased proportionally to the increase in the output voltage signal of said amplifier 'above' a predetermined value so that with increasing input voltage to said amplifier the time constant of the AVC cir-v arres s

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Control Of Amplification And Gain Control (AREA)
  • Amplifiers (AREA)
  • Control Of Eletrric Generators (AREA)
US00052814A 1969-07-07 1970-07-07 Amplifier with improved avc circuit Expired - Lifetime US3716801A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE1934306A DE1934306C3 (de) 1969-07-07 1969-07-07 Selbsttätig geregelter Wechselspannungsverstärker mit einer merklichen Zeitkonstante des Stellgliedes

Publications (1)

Publication Number Publication Date
US3716801A true US3716801A (en) 1973-02-13

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ID=5739066

Family Applications (1)

Application Number Title Priority Date Filing Date
US00052814A Expired - Lifetime US3716801A (en) 1969-07-07 1970-07-07 Amplifier with improved avc circuit

Country Status (4)

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US (1) US3716801A (enExample)
DE (1) DE1934306C3 (enExample)
FR (1) FR2056454A5 (enExample)
GB (1) GB1312930A (enExample)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3790896A (en) * 1972-01-11 1974-02-05 Sony Corp Automatic gain control circuit
US4591733A (en) * 1982-01-15 1986-05-27 Licentia Patent-Verwaltungs-Gmbh Circuit arrangement for generating a control voltage which is dependent upon an alternating voltage

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5515857U (enExample) * 1978-07-17 1980-01-31

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2692306A (en) * 1949-12-08 1954-10-19 Rca Corp Audio amplifier with plural automatic gain controls
US2799737A (en) * 1944-08-30 1957-07-16 Stanley R Rich Automatic volume control for amplifiers
US2858424A (en) * 1954-10-01 1958-10-28 Gen Electric Transistor amplifier with automatic collector bias means responsive to signal level for gain control
US3449684A (en) * 1966-10-24 1969-06-10 Sholly Kagan Audio compression amplifier

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2799737A (en) * 1944-08-30 1957-07-16 Stanley R Rich Automatic volume control for amplifiers
US2692306A (en) * 1949-12-08 1954-10-19 Rca Corp Audio amplifier with plural automatic gain controls
US2858424A (en) * 1954-10-01 1958-10-28 Gen Electric Transistor amplifier with automatic collector bias means responsive to signal level for gain control
US3449684A (en) * 1966-10-24 1969-06-10 Sholly Kagan Audio compression amplifier

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3790896A (en) * 1972-01-11 1974-02-05 Sony Corp Automatic gain control circuit
US4591733A (en) * 1982-01-15 1986-05-27 Licentia Patent-Verwaltungs-Gmbh Circuit arrangement for generating a control voltage which is dependent upon an alternating voltage

Also Published As

Publication number Publication date
DE1934306A1 (de) 1971-01-21
FR2056454A5 (enExample) 1971-05-14
DE1934306C3 (de) 1975-06-12
DE1934306B2 (de) 1972-05-04
GB1312930A (en) 1973-04-11

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Legal Events

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AS Assignment

Owner name: TELEFUNKEN ELECTRONIC GMBH, THERESIENSTRASSE 2, D-

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:LICENTIA PATENT-VERWALTUNGS-GMBH, A GERMAN LIMITED LIABILITY COMPANY;REEL/FRAME:004215/0210

Effective date: 19831214